Circuit breaker



FIG. 1 is an isometric view of our design for a circuit breaker;

FIG. 2 is a front view thereof; and

FIG. 3 is a rear view thereof;

FIG. 4 is a left side view thereof;

FIG. 5 is a bottom view thereof;

FIG. 6 is a right side view thereof; and,

FIG. 7 is a top view thereof.

The parts shown in broken lines form no part of the claimed design. 

The ornamental design for a circuit breaker, as shown and described. 